Successful operation of a radar altimeter requires that the device is able to detect and track the reflected return of its own transmitted radio frequency (RF) signal, without being negatively impacted by interference signals in the same RF band. This in-band interference may cause the victim altimeter to track the false signals and report erroneous altitudes, or to lose track of its own signal and “break lock.” Both of these failure modes are problematic, and in safety-critical applications such as final approach guidance or terrain avoidance, they are highly dangerous as well. The most common sources of in-band interference signals are other radar altimeters. In certain applications, multiple radar altimeters of the same type may be installed on the same aircraft for redundancy, leading to potential issues of mutual interference between the devices. In addition, the radar altimeters installed on other aircraft, which may be of the same type or a different type, may pose a threat under certain circumstances, especially in high-traffic airspace such as in the immediate vicinity of busy airports.
Many known techniques exist to prevent radar altimeters from tracking false signals from other altimeters of a different type. In the case of frequency-modulated continuous wave (FMCW) radar altimeters, which represent a majority of the altimeters used in commercial applications, selecting a sweep rate sufficiently different from those used by other altimeter products may be enough to suitably limit the susceptibility to interference from these other products. The issue of mutual interference between altimeters of the same type, however, is often a more difficult problem to solve. Addressing this issue may require more subtle or sophisticated methods to reduce interference susceptibility and mitigate the impact of interference.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a system that efficiently and effectively prevents interference in a radar altimeter.